I did use stock pushrods, but, stock heads were also shaved .030, and stock gaskets were replaced with fel-pros. between the 2, I took out .050" of required pushrod length.

Now that I have edelbrock heads on the motor, I have adjustable roller rockers

If you're loose, You probably need longer pushrods. stock cam has like, .420 lift? that 5.9 whiplash has .544 lift.